A global war will ruin the civilization

H.G. Wells : science fiction writer
A global war will begin in 1940. This war drags out over many decades until most of the people still alive (mostly those born after the war started) do not even know who started it or why. Nothing will be manufactured at all any more and society will be broken down into primitive localized communities. In 1966 a great plague will wipe out most of what people are left but small numbers still survive. One day a strange aircraft lands at one of these communities and its pilot tells of an organization which is rebuilding civilization and slowly moving across the world re-civilizing these groups of survivors. Great reconstruction will take place over the next few decades and society is once again great and strong.

Novel "The Shape of Things to Come"